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Monday, August 27, 2018

Large Segmented Bowl - #5 Adding Rings & Fitting the Halves


To start working down from the top I need to build a base similar to what had been done for the bottom layers.  I keep a lot of odds and ends from various projects hoping to be able to use them elsewhere and this just happened to be an occasion where I could.  When I made the Snare Drum I built a multilayer base and could now re-purpose two of those layers to act as my base. 

Since the large face plate is in use and I am not going to take it off until the turning is done I used my smaller faceplate.  In the photo below starting at the top of the clamped stack you can see the smaller black 3” diameter black face plate just peeking out behind one of the clamps.  It has been screwed to an MDF layer which in turn is screwed but not glued to a segmented pine ring.  The MDF and Pine ring are not glued together so I can take the MDF piece off and check the joint between the top and bottom sections.  I will take a photo when I get there so if it does not make sense now it should then.  The top ring of the bowl (on the bottom of the stack) is centered on the Pine ring then glued in place which is what is going on in this photo.  Note the top ring like the bottom ring is made up of only cherry segments.  That’s a design choice to act as a visual cap on the bowl, or at least that is what it is supposed to do.
 
The photos below show, just like before the rings being added and the interior face being worked into final shape is stages.

After adding one more ring, the fourth and last one I spent quite a bit of time going back and forth between the two halves measuring and refining the joint where the top and bottom will be mated.  Not only do I need to match the inside diameter I need to make sure the curve flows across the joint.  That curve whose radius changes as is goes across the two rings to be mated has to look and feel continuous.  When I got to a point where things looked like they might match up I took the stack off the lathe, unscrewed the MDF disk from the Pine ring and set it next to the bottom half.  This photo shows how removing the MDF disk allows access to the inside which will enable me to check how well the two halves come together.

Setting the top section on the bottom and aligning them gives a rough idea of the bowl profile.

With the top in place I could see how close I got to matching the two halves.  It was really pretty close, better than I had hoped for a first attempt. 

Once I had checked out the joint and made some marks to indicate what additional shaping needed to be done I pulled the top off and screwed the MDF disk back on.  Below is just before aligning the top and screwing it back in place.  The green mark on the Pine ring and the MDF is my reference mark so things go back together the way them came apart.  There is also a blue one on the opposite side. 

You would think that using the reference marks then screwing the MDF disk back in the exact location where it came off would automatically center everything allowing me to go right back to turning.  That’s what I thought too, but was wrong.  There is just a little bit of wiggle room even using eight screws and putting the disk back in the same place.  To correct I just snugged two screws down then mounted the stack back on the lathe.  With that done the tool rest is set so it just touched the edge of the 4th ring.  Then as I spun the stack I could see what adjustments needed to be made to center the stack.  It took a little time but ended up just fine. 

I worked to match the exterior diameter of the bottom ring of the top stack to the top ring of the bottom stack which is pretty easy.  It just requires a light touch with the tools and frequent stops to measure so as not overshoot.  The inside diameter also needs to match up and the aforementioned curve has to flow across the joint.  It is sort of like a real marriage.  When it’s good it’s very good and when it’s bad it’s a disaster. 

A couple of fittings which required going through the steps of taking the MDF disk on and off got me very, very close.  The inside of top stack has just a tiny lip overhanging the bottom.  I think I will leave it that way and do the final work after the two stacks are glued together.  Below is a photo that shows how the two stacks match up with the red arrow pointing at the joint.  This is the photo I was referring to when I was talking about gluing the 1st ring on in the second paragraph.

At this point I am almost ready to glue the two halves together.  To help minimize any problems with glue removal I am going to put two coats of finish on the inside before gluing the two halves together.  With the finish on it will be much easier to do any cleanup afterwards.   However, this means that I have to have the inside completely done and sanded.  I start with 120 grit sand paper and work my way up through 320 grit.  Here is what the halves look like ready to finish.

I debated on the finish for a while but finally decided to use Danish Oil Finish.  It should give me a nice low-luster finish bringing out the grain of the cherry and walnut.  Below is the top stack showing the first wet coat of the oil on half of the piece.  I will put two coats on then glue the halves together.

Next up – Gluing the Halves Together & Turning the Outside

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